This invention relates to a method of cleaning porous ceramic filters that is applicable to filtration equipment that is capable of effectively removing organics, inorganics and other impurities from pool water and other kinds of contaminated water. The invention also relates to a circulating purification apparatus and a pool water purifying apparatus that use a circulating system which, with the aid of backwashable porous ceramic filters, is capable of effectively removing organics, inorganics and other impurities from circulating water such as pool water and other kinds of contaminated water. The invention also relates to a system of purifying pool water using those apparatus.
More particularly, this invention relates to an apparatus for purifying pool water in a circulating manner which, after being assembled in a factory, can be divided into components that can be transported on vans and other vehicles and that can be reassembled on an installation site by connecting them to a desired layout of external piping in a very simple way. The invention also relates to a pool water purifying apparatus that can be used with an ultrafiltration means to insure high performance over an extended period. The invention also relates to a pool water purifying apparatus that is an integral assembly of a porous ceramic filter, an adsorptive purifier, a disinfecting means and other purifying means, and even an ultrafiltration means and which yet is compact and can be installed by simple work. The invention further relates to a system for purifying the water in a plurality of pools including outdoor pools, indoor pools and whirlpools.
The term "pools" as used herein includes not only ordinary swimming pools but also whirlpools installed in sports clubs, Kurhaus (spa houses) and healthcare facilities, as well as various kinds of health promoting hot tubs and spas.
With the growing concern for physical fitness, many people prefer swimming as an exercise of the whole body that helps promote their health and relieve psychical stress and today an increasing part of the population, irrespective of age and sex, frequently go to swimming pools. In order for people to enjoy swimming in a safe and clean condition, pools must be kept clean, particularly in terms of water quality, and as the use of swimming pools increases, the performance requirements of purifying facilities that determine the quality of pool water are becoming increasing stringent. This is particularly true with indoor pools which are supposed to be used in all seasons because sweat, hair and other foreign matter originating from the human body are potential sources of bacterial growths that contaminate the pool water and deteriorate its quality.
Filtration equipment available today adopts various methods to purify pool water. A common method is based on the combination of filtration and disinfection with chlorine or its compounds. Recently proposed methods are disinfection with ultraviolet rays and treatments with ozone. New filter media have also been proposed as substitutes for sand and they are porous filter media exemplified by ceramic filters and activated carbon (see Japanese Patent Application (kokai) No. 143917/1988 and Japanese Patent Application Nos. 311319/1988, 311320/1988, 126035/1989 and 126036/1989).
One of the filter media that are drawing particular attention for application to facilities for purifying pool water is a porous ceramic filter. Porous ceramic filters have a three-dimensional network of extremely fine filtering spaces that are advantageous for application to pools, particularly to indoor pools, and are capable of effectively trapping organic matters such as oils excreted from the human body that have cannot be removed with existing filters.
The concept of prior art pool water filtering equipment that employs porous ceramic filters is shown in FIG. 26. A cylindrical porous ceramic filter 700 (hereunder referred to simply as "ceramic filter 700") is closed on its top with a lid 702 and fixed in the center of a hollow cylindrical housing 704.
An entrance line 708 for introducing water from a pool 706 is connected to the left side wall of the housing and an exit line 710 for recirculating filtered water to the pool 706 is connected to the center of the bottom of the housing 704. A line 712 for introducing filter aids is connected to the right side wall of the housing 704; an air vent 714 is provided on top of the housing 704; and a drain line 716 is connected to the bottom of the housing 704 in a position outside the ceramic filter 700. A back wash line 718 for cleaning the ceramic filter 700 is provided as a branch from the exit line 710.
The process of filtering the water in the pool 706 with the filtration equipment shown in FIG. 26 proceeds in the following manner. First, the air vent 714, a valve 720 on the back wash line 718 and a valve 722 on the drain line 716 are closed. Then, a valve 724 on the entrance line 708 and a valve 726 on the exit line 710 are opened and a circulating pump 728 is driven so that the water in the pool 706 circulates through a loop consisting of the entrance line 708, housing 704 and exist line 710 in that order. In short, as the water passes through the ceramic filter 700 in the direction a of a solid arrow, impurities in it are removed by filtration and clean water is returned to the pool 706.
As this process of water filtration continues, filter cake builds up on the outer surface of the ceramic filter 700 and clogs its extremely fine voids. If this condition occurs, the filter efficiency will decrease and, in an extreme case, it becomes necessary to replace the whole unit of expensive ceramic filter 700 but this means an extremely high cost since a number of filter units are usually employed.
To avoid this problem, it is necessary to clean the ceramic filter 700 periodically by removing the filter cake deposited on its outer surface. Cleaning of the ceramic filter 700 is conventionally performed by backwashing in which a "jet stream" consisting of a mixture of cleaning water and air is supplied at high speed through the back wash line 718 in such a way that the jet stream coming into the ceramic filter 700 passes through it to go outside as indicated by an unfilled arrow b.
As shown in Japanese Patent Application (kokai) No. 2252/1973, the back wash line 718 is furnished with a large air tank 729 filled with a large amount of air compressed to a comparatively high pressure and a flush tank 730 partly filled with cleaning water A to one third of its capacity. When a valve 732 provided between the two tanks is opened, the large amount of compressed air in the air tank 729 is jetted into the flush tank 730, where it is mixed with the cleaning water to produce an accelerated jet stream which is introduced into the ceramic filter 700.
The process of backwashing for cleaning the ceramic filter 700 in the apparatus shown in FIG. 26 starts with stopping the circulating pump 728, closing the valves 724 and 726 and opening the valves 720 and 722. This completes the preconditioning step. Then, the valve 732 is opened, whereupon the large amount of compressed air in the air tank 729 is jetted into the flush tank 730 and the resulting accelerated jet stream flows through the back wash line 718 in the direction of arrow to come into the ceramic filter 700 through which it passes (for backwashing) in the direction indicated by an unfilled arrow h and, after dislodging the filter cake and other deposits on the outer surface of the filter 700, the jet stream leaves the housing 704 via the drain line 716.
Since the voids in the ceramic filter 700 are extremely small, the jet stream used for backwashing is required to have a very high flow rate, namely, high cleaning pressure, in order to insure efficient cleaning of the filter. To this end, the air tank 729 must be filled with a large amount of highly compressed air but then the air tank 729 and, hence, the overall filtration equipment, becomes bulky to increase the initial investment cost.
Further, the ceramic filter 700 must be backwashed at an adequate cleaning pressure for a comparatively long period in order to insure positive cleaning of the filter.
However, as described above, the prior art backwashing apparatus forms a jet stream using the highly compressed air contained in the air tank 729 of a predetermined capacity, so the cleaning pressure drops in a very short time after it peaks (see FIG. 7). Hence, in order to maintain the necessary cleaning pressure for a desired period of time, not only a very large air tank 729 but also a high-performance system for filling with compressed air is necessary. In addition, the cleaning water must be supplied in a large volume. These result in a further increase in the equipment and running costs.
Existing apparatus for filtering pool water and industrial water are commonly equipped with many tanks including filtration tanks and disinfection tanks and fluids to be filtered such as pool water and contaminated water must be circulated through those tanks. To meet this need, a circulating system is constructed by interconnecting those many tanks via pipes. The circulating system used in existing filtration apparatus is not only used for recirculating the fluids but also equipped with a bypass line, a wash line and a backflow line that permit the interior of tanks to be washed and which, if necessary, permit the circulating fluids to bypass certain tanks or flow backward.
A prior art circulating system that has these capabilities is shown by 800 in FIG. 27 and comprises the following components: tanks 802a, 802b and 802c; an inlet pipe 804a and an outlet pipe 806a that are connected to each tank; a main pipe 808 that is directly connected to pipes 804a and 806a; switch valves 810a and 812a provided on the main pipe in two opposite positions with respect to the junction with the inlet pipe 804a; and a switch valve 814a provided on the outlet pipe 806a (those pipes and valves constitute a circulation line 816); a bypass line 818 formed of a separate bypass pipe 820; and a switch valve 822a provided on the bypass pipe 820 in positions that correspond to the respective tanks 802a, 802b and 802c in such a way that the main pipe 808 is connected to the bypass pipe 820 in two opposite positions with respect to the switch valve 822a. Because of this layout, the circulation line 816, bypass line 818 and a backflow line 824a can be selectively activated depending on the need.
Another prior art circulating system is shown by 850 in FIG. 28. A first tank 852a has an outlet pipe 856a that is fitted with a switch valve 854a and which is connected to a main pipe 862 which in turn is connected to an inlet pipe 860b that is fitted with a switch valve 858b and which is connected to a second tank 852b, whereby a circulation line 864 is formed. A bypass line 868 is formed of a separate bypass pipe 866. The circulation line 864 and the bypass line 868 are interconnected by a pipe 870a which is fitted with a switch valve 872a. The bypass pipe 866 is also fitted with a switch valve 874a in a position that corresponds to the first tank 852a. The second tank 852b is connected to a third tank 852c in the same manner as described above to form both a circulation line and a bypass line.
When these circulating systems are to be applied to a circulating filtration apparatus, it is necessary to provide not only a bypass pipe in addition to the main pipe but also the number of switch valves that permit the circulation line, bypass line and backflow line to be selectively activated increases. As a result, the number of components increases to make the layout of the overall equipment too complicated and costly to realize a compact system. Furthermore, great complexity is involved in controlling the switch valves for selectively activating the various lines.
When a new pool is to be constructed, the installation of a purifying apparatus on the site is desirably performed as simply as possible and completed within the shortest possible period so that the progress of other building operations including the construction of the pool itself will not be retarded. This is also true with tie case of replacing an existing pool water purifying apparatus with a new one. Particularly in the case of indoor pools which are supposed to be used in all seasons, meeting that need is important for shortening the "closing time".
Ideally, a purifying apparatus as assembled in a factory is transported to the construction site where it is installed and connected to the pool or drain facilities. In fact, however, apparatus for purifying pool water, in particular those of high performance which have an excellent purifying capability, are bulky and involve various kinds of difficulty such as the need to use large a transportation means. Further, the purifying apparatus is to be used with proper connection being made not only to the pool but also to drain and water supply facilities on the site, so various devices and pipes associated with the purifying apparatus must be fabricated to insure good match with those facilities. Therefore, in practice, it is considerably difficult to transport the pool water purifying apparatus in the same condition as it was assembled in a factory and to place it on the installation site.
Therefore, the conventional practice currently adopted is to assemble a filtration device, a disinfecting device and other individual components of the pool water purifying apparatus, transport them separately to the installation site and combine them into a complete system. However, the pool water purifying apparatus is usually installed in a fairly narrow limited place and, as already mentioned before, it comprises many components including various kinds of disinfecting and adsorbing devices and a complicated piping system is necessary to interconnect these components. Further, the use of machines and tools such as a crane and a hoist is also limited for working on the installation site. Under these circumstances the on-site operation of installing the purifying apparatus is time-consuming and difficult to accomplish.
In existing purifying apparatus, especially one that adopts filtration equipment using ceramic filters, fine particles in pool water and other kinds of water to be treated, such as organic matters with a particle size of 0.5-1 .mu.m and above, as well as fine particulate organics including some bacterial species are removed by the filtration equipment and those bacteria which cannot be removed by the filtration equipment are disinfected with a disinfecting device, whereas malodor substances such as ammonia contained in sweat and dead bacterial cells are removed by an adsorbing device. The bacteria range approximately from 0.2 .mu.m to 1 .mu.m in size, so they can be effectively removed in the existing purifying apparatus by using ceramic filters and can be killed almost completely by means of the disinfecting device.
However, viruses that cause serious diseases such as AIDS, hepatitis, influenza and Japanese B encephalitis are in the form of colloidal particles ranging from 0.01 .mu.m to 0.2 .mu.m in size and cannot be removed even if ceramic filters are used. Needless to say, ceramic filters are totally ineffective for removing smaller particles such as protein particles with a size of ca. 0.001-0.01 .mu.m.
With the growing concern of the public for health, the number of healthcare facilities including sports clubs, health resorts furnished with multi-purpose spas (hot tubs), Kurhaus (spa houses) and healthcare centers is increasing today. These healthcare facilities are furnished with many kinds of pools including swimming pools, Jacuzzi whirlpools such as and jet baths and various other spas and hot tubs, among which visitors can select suitable ones to meet their object. Since safety and cleanness are two absolute conditions that must be satisfied by healthcare facilities, it is necessary that the pools in those facilities be strictly checked for their cleanness, particularly the quality of pool water. To meet this need, the performance requirements of purifying facilities that determine the quality of pool water are becoming increasingly stringent and modern versions are designed to have better performance in a correspondingly large size.
A pool water purifying apparatus is an expensive system that is generally composed of filtration equipment that removes various impurities such as dust and hair contained in pool water, adsorptive purifying equipment that removes oils and other fine impurities, disinfecting equipment that disinfects pool water, optional equipment that supplies filter aids to the filtration equipment, means of heating pool water (in the case of indoor pools and hot tubs), pipes that interconnect these many units of equipment, and a control unit that control these devices. A high-performance purifying apparatus is particularly expensive and large in size and its installation takes much time.
However, filters and other purifying elements used in the existing purifying apparatus are susceptible to changes in temperature and other factors and the purifying capability of the apparatus will fluctuate or deteriorate to thereby make it impossible to purify different kinds of pool water by means of a single unit of the apparatus. Under these circumstances, Kurhaus and other facilities that use many pools require a number of expensive pool water purifying apparatus and it is sometimes necessary to install as many purifying apparatus as the pools used, and this renders the investment, construction and running costs of the purifying system only exorbitant.
The situation may be better understood by the following example. Not all pools used in Kurhaus have the same water temperature. Swimming pools, even if they are indoor pools, have water temperatures of about 30.degree. C. whereas the water in Jacuzzi is about 40.degree. C. and hot tubs and spas have much higher water temperatures. However, the performance of existing purifying apparatus varies with the temperature of water and no single unit of purifying apparatus is capable of keeping a plurality of pools in a uniformly clean condition. Further, depending on size, the performance of existing purifying apparatus is such that it is difficult to purity the water in a plurality of pools and keep them clean. Therefore, more than one unit of purifying apparatus is necessary to cope with different water temperatures and, as a result, the overall cost of the purifying system and its running cost become exorbitant.